The long term objective of this proposed research is to enhance our understanding of spontaneous diarrhea caused by Clostridium difficile in aged hamsters. The immediate objective is to study the host responses of aged hamsters to experimental C. difficile infection and to the exotoxins of this bacterium. There are 4 specific aims: (1) To study the host responses of aged hamsters to C. difficile infection, (2) To compare the efficacy of microbiological isolation and identification with that of detection of toxin-A by enzyme immunoassay and toxin-B by tissue culture cytotoxicity assay, (3) To study flora changes during C. difficile infection and to explore the use of DNA hybridizational technique as a tool for enumeration of predominant flora, and (4) To study the host responses of aged hamsters to the exotoxins of C. difficile. To achieve specific aim 1, 132 retired breeders of both sexes will be used in 11 experimental groups to examine the susceptibility of aged hamsters to varied doses of inciting antibiotic - clindamycin - and simultaneous ingestion of C. difficile. The objective of specific aim 1 is to answer the question whether the same type of proliferative caecitis and colitis can be reproduced experimentally. For specific aim 2, a comparison of 3 detection methods is proposed. The routine microbiological isolation on CCFA agar, detection of toxin A by EIA and detection of toxin B by cytotoxicity. This experiment will help us to device better means of detection of C. difficile. For specific aim 3, a novel approach in the enumeration of predominant flora is proposed. A DNA hybridizational technique is used to estimate population level of a predominant bacterial species, Bacteroides ovatus, in the ceca of affected hamsters. And finally for specific aim 4, hamsters will be injected intracecally and intravenously (portal vein) of both exotoxins to produce the typical lesions in the ceca and to answer the question of the relationship between cholangiohepatitis and glomerulonephritis to C. difficile infection. The completion of these 4 experiments will provide scientific data to enhance our understanding of the disease induced by C. difficile and to device ways and means to limit the potential effects of this disease on experiments that require the use of hamsters housed for prolonged period in the laboratory.